Electromagnet structure



Sept. 17, 1935, B, M, CNN 2,014,880

ELECTROMAGNET STRUCTURE Filed Aug. 12, 1955 VOLTS CURRENT Inventor:

Berrward IVLC 'n, b {)4 6.8%

Hi5 ttorne l Patented Sept. 17, 1935 PATENT OFFICE ELECTROMAGNET STRUCTURE Bernard M. Cain, Ballston Lake, N. Y., assignor to General Electric Company, a corporation of New York Application August 12, 1933, Serial No. 684,885

9 Claims.

My invention relates to electromagnet structhe invention which is described and claimed in a joint patent application of Benjamin R. Teare,

Jr. and Max A. Whiting, Serial No. 642,736, filed November 15, 1932, and assigned to the assignee of the present application. In that application there is disclosed a generator voltage regulator which is arranged to hold substantially constant voltage up to a predetermined value of generator current whereupon with further increases in current the voltage droops relatively abruptly. This relatively abrupt droop is produced by means of a variable reluctance mag-' netically saturable element and it is pointed out in that application that as this element necessarily has some reluctance even when unsaturated, a-

slight voltage droop tends to be produced even before the element becomes saturated. Several different ways of compensating for this slight droop are disclosed in that application, but I have found that all of these means produce a compensating efl'ect which varies in a substantially linear manner with the current and as the droop which is tobe compensated for varies in a non-linear manner in accordance with the saturation characteristic of the saturable element, as complete compensation as might .be desired is not produced.

In accordance with my invention I provide compensating means for the voltage droop caused by the reluctance of the saturable element during the early stages of its saturation by means which acts in a non-linear manner, such for example as by an additional magnetically saturable element. In this manner I found it is possible to achieve substantially complete compensation so that, up to' the predetermined current value at which it is desired to produce a relatively abrupt droop in voltage, the voltage will remain substantially constant.

An object of my invention is to provide a new" A further object of my invention is to provide an improved voltage regulator which acts to hold substantially constant voltage up to a predetermined value of current after which the current droops relatively abruptly.

My invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing, Fig. 1 is a diagrammatic show- 5 ing of an embodiment of my invention as applied to the electromagnet structure of a generator voltage regulator, and Fig. 2 is a set of curves for illustrating the operation of my invention.

Referring now to Fig. 1, a main electromagnet core I is provided which is arranged to be excited by a voltage-responsive main control winding 2 and which has an armature 3 which is mounted on a suitable resilient biasing spring 4. Air gaps 5 and 6 are provided between the core I and the armature 3. A pair of control contacts, one of which is on armature 3 and the other of which is fixed are provided, and these contacts are arranged to separate when armature 3 is attracted to the core member l.

The means for causing the relatively abrupt droop in regulated voltage with increases in current beyond a predetermined value comprises a core member 8 which is arranged to be excited 5 by a current winding 9 thereon. As shown, member 8 is in the form of a yoke and this member cooperates with a saturable section or element l2 of the core I, which element is shown as a restricted section of the core. Air gaps I0 and II are provided between the member 8 and the core I.

Inserted in the air gap H is a magnetically saturable element ll, such as a section of iron. The purpose of this element, the operation of which will be explained more in detail later, is to produce the compensating effect of my invention.

The regulator is shown as arranged to regulate the voltage of a shunt type generator I3 having a shunt field winding M in series with which is a regulating resistor Hi. The generator 13 is shown connected to charge a storage battery It. The electrical connections between the regulator and the generator are such that the contacts I u are connected across the regulating resistance l5 so as to short circuit this resistance when the contacts are in engagement. The voltage responsive main control coil 2 is connected across the generator I3 and the current responsive winding 9 is connected in series with the generator.

The general operation is as follows: Assume that generator. I3 is being driven by any suitable prime mover (not shown) and that the generator load circuit is either open or the current therein I is negligible. Under these circumstances, the effect of the current responsive element of the regulator may be ignored and only the voltage Winding 2 will be active. As shown, the contacts I are in engagement thereby short circuiting the resistance I5 and causing a maximum current to flow through the field winding II. This increases the voltage of generator I3 until the voltage reaches such a value at which the energization of winding 2 produces suilicient flux to cause a pull on the armature 3 which exceeds the counterpull of the biasing spring 4, thereby separating the contacts I. As soon as the contacts I separate, the resistance I5 is in series with the winding I4 and the current in the field winding decreases, thereby decreasing the voltage of generator I3 and consequently decreasing the energization of winding 2. This weakens the pull of the magnet and the spring 4 snaps the contacts I closed. The cycle then repeats itself and this continues at a relatively high rate of speed whereby a substantially constant voltage of generator I3 is maintained.

The operation of the current responsive voltage droop producing feature of the regulator is as follows: As shown, the winding 2 is so connected and wound that it produces a flux which flows through the core I and the armature 3 in a counter-clockwise direction. The current winding 9 is so connected as to produce a flux in the core member 8 and the saturable section I2, which is also in a counter-clockwise direction. At low current values this flux merely circulates through the core 8 and the restricted section I2 and as this section has a relatively low reluctance practically all of the flux is by-passed through this section and but a very small portion of the flux flows through the magnetic circuit including the armature 3, because of the fact that the air gaps 5 and 6 are made substantially greater than the air gaps III and I I so that the reluctance of the path through the restricted section I2 is considerably less than the total reluctance of the path through the armature and the air gaps 5 and 6. However, as the generator current increase saturation takes placed in the restricted section I! with the result that its magnetic reluctance increases. The result 01' this action is that a greater and greater percentage of the flux produced by the winding 9 will tend to flow across the air gaps 5 and 6 and through the armature 3. As the direction of this flux will be the same as the direction of the flux produced by the winding 2, the winding 2 will require less energization to maintain the same value of total flux across the air gaps 5 and 6 and as the action of the regulator is to try to maintain a constant value or flux across these air gaps the result will be that the regulated voltage will decrease.

As explained in the above referred to joint patent application; it has been found that even though the reluctance of section I2 islow at low current values, nevertheless, it is appreciable, so that an appreciable amount of flux crosses the air gaps 5 and 6 and traverses the armature 3. This causes a change in calibration of the regulator resulting in an objectionably premature voltage droop but it was found that by properly proportioning the air gap II, suilicient leakage flux would be produced by the reluctance of the air gap II to produce partial compensation for this droop. The action of this leakage mix is such that it enters the sides and ends oi the armature 3 adjacent its contact I and then, returns through the air gaps 5 and 5 in parallel.

The flux returning through the air gap 5 will be cumulative with respect to the main flux while the flux returning through the air gap 6 will oppose the main flux and as the reluctance of gaps 5 and 6 is substantially equal, the leakage flux will divide substantially equally between these two air gaps. Due, however, to the fact that air gap 6 is further away from the effective pivot 01' the armature than air gap 5 the effect of the leakage flux will be stronger at air gap 8 than at air gap 5, and as the efiect is to weaken the pull of the main magnet at air gap 6 and to strengthen it at air gap 5 the total eflect of the leakage flux will be to weaken the pull on the armature 3 as the current increases, and this tends to compensate for the increase in flux through the air gaps G and 5 caused by the reluctance of section I2 at low current values.

I have found, however, that the above described compensating action of the leakage flux caused by a proper proportioning of the air gap II has a substantially linear eiIect with changes in current, whereas the droop producing effect of the reluctance of section I2 is non-linear. Consequently it is impossible to secure correct, or substantiallycomplete, compensation with such an arrangement. However, I have found that by inserting a magnetically saturable element, such as an iron member "in the air gap II, I can secure substantially complete compensation.

The action of section I1 is as follows: During low current values element I1 is unsaturated and air gap I I is substantially magnetically short circuited so that there is substantially no leakage flux produced, which is as it should be because at very low current values I have found that the reluctance of the section I2 is so low as to be negligible. However, at intermediate values of current between these extremely low values and the predetermined high value at which the relatively abrupt voltage droop is to occur, the element I'I begins to saturate thereby increasing the reluctance of this element and producing the equivalent of an air gap at I I. Consequently, leakage flux is produced and this flux tends to compensate for the increasing reluctance oi the section II, as it begins to saturate with increases in current. Consequently, as the droop producing action or the increasing saturation of the restricted section II, and the compensating action 01' the leakage flux producing saturable element I1, both operate on the principle of saturation and are both non-linear, they tend more nearly to neutralize each other throughout the range of intermediate current values. When the predetermined high value 01' current is attained the element Il becomes practically completely saturated, and hence it has little or no eiiect in increasing the leakage flux so that the further saturation of the element I2 produces the desired relatively abrupt droop in voltage.

In Fig. 2, the solid curve shows the improved characteristic obtained by my invention. As shown, the section abc o! the curve is substantially a straight horizontal line showing that substantially constant voltage is maintained over the desired current range, and for current values above 0 there is a relatively abrupt droop in voltage. The upper dotted curve shows the type 01 characteristic which would be obtained if the element I1 were omitted. In that curve the action 01' the leakage flux produced during the low and intermediate values of current by the relatively high reluctance of the air gap II is such as to overcompepsate for the low values of reluctance of section I! and consequentlya voltage rise is obtained. The lower dotted curve shows the characteristic which would be obtained if the air gap II were omitted entirely and there were no saturating element l1. This curve shows that beyond very low values of current the gradually increasing reluctance of the section II before it reaches the knee of its saturation curveis suflicient to produce an objectionable premature voltage droop.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention and I therefore aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, an electromagnet armature and two magnetic circuits each including said armature, one of said circuits having a variable reluctance magnetically saturable flux by-pass around said armature, said one circuit also including a variable reluctance magnetically saturable element whereby a controlled leakage flux threading the other circuit is produced.

2. In combination, an electromagnet armature and three magnetic circuits each including said armature, the first circuit including a variable reluctance magnetically satmable section, the second circuit utilizing said section as a flux bypass around said armature, the second circuit including a magnetically saturable element, and the third circuit containing leakage flux from the second circuit which varies with the reluctance of said saturable element.

3. In combination, an electromagnet compris ing a core member, an armature and ,a direct current exciting winding, an additional electromagnet comprising an additional core member, a part of the first core member, an additional direct current exciting winding and a magnetically saturable element. said additional electromagnet and said saturable element being so arranged with respect to the first electromagnet that when said element saturates it produces a leakage flux from said additional electromagnet which acts on the armature of the first electromagnet in a manner ing for producing a flux in said second core member which traverses said portion of said first core member in a direction opposite to said first mentioned flux, and a magnetically saturable element in the path of said last mentioned flux 5 where it enters said first mentioned core member.

5 A voltage regulator having, in combination, current responsive means including a magnetically saturable element for changing the calibra' tion of said regulator with changes in current in 10 accordance with the magnetic saturation of said element, and means including a second magnetically. saturable element for neutralizing the calibrating eifect of said current responsive means during the early stages of the saturation of the 15 second saturable element.

6. A vibratory contact generator voltage regulator having, in combination, current responsive flux producing means including a magnetically saturable element for reducing the voltage which 20 said regulator will hold as the current increases in accordance with saturation of said element, and means including a second saturable element for producing a controlled leakage of the flux produced by said current responsive means which is 25 sufficient to neutralize the efiect of said first saturable element during the early stages of its sat uration.

o 7. In combination, a direct current shunt generator, a vibratory contact voltage regulator for 30 to weaken the action of the first electromagnet thereon.

4. In combination, an electromagnet core having two pole faces, an armature cooperating with said pole faces, an effective pivotal support for said armature nearer one end thereof than the other, a direct current energized winding for producing a flux which enters said armature from the pole face of said core which is farthest away from said support, a second core member whose magnetic circuit includes a portion of said first core member which is adjacent said last mentioned pole face, a direct current energiz'ed windsaid generator, means including a magnetically saturable element responsive to the current of said generator for causing the voltage held by said regulator to droop as the current increases,

1 and means including another magnetically sat- 35 urable element for substantially neutralizing the efiect of said current responsive means at current values below a predetermined value.

8. An electric regulator having an operating element, a voltage responsive means for producing a magnetic flux for actuating said operating element, a current responsive means for modifying the magnetic flux produced by said voltage responsive means non-linearly with the current traversing said current responsive means, and means in operative relation with said current 'responsive means for varying its modifying action non-linearly with the, current traversing said current responsive means.

I 9. In a regulator having voltage responsive 50 means and current responsive means cooperating for causing said regulator to hold a substantially constant voltage up to a predetermined value of current traversing said current responsive means and wherein said current responsive means .causes a non-linear drop in the value of voltage BERNARD M. CAIN. 

